1. Field of the Invention The present invention relates to a Multiple Input Multiple Output (MIMO) wireless communication system. More particularly, the present invention relates to an apparatus and method for performing beamforming in a MIMO wireless communication system.
2. Description of the Related Art
With the growing demand for high-speed, high-quality data transmission, a Multiple Input Multiple Output (MIMO) wireless communication scheme using a plurality of Transmit (Tx)/Receive (Rx) antennas has drawn attention as one technique that is capable of satisfying such a demand. In the MIMO scheme, communication can be performed using a plurality of streams through a plurality of antennas. Therefore, in comparison with the conventional technique using a single antenna, channel capacity can be significantly increased when using the MIMO scheme. For example, if a transmitting end and a receiving end use M Tx antennas and M Rx antennas, a channel between the antennas is independent, and a bandwidth and entire Tx power are fixed, then an average channel capacity is increased M times higher than the case of using the single antenna.
The MIMO scheme can be classified into a Single User MIMO (SU MIMO) and a Multiple User MIMO (MU MIMO). The SU MIMO denotes the use of a pair of transmitting/receiving ends to perform one-to-one communication by occupying all of a plurality of channels created by a plurality of antennas. The MU MIMO denotes the divided use of the plurality of channels created by the plurality of antennas to perform communication between the transmitting/receiving ends having a one-to-one relation.
When one Base Station (BS) and a plurality of Mobile Stations (MSs) perform communication simultaneously according to the MIMO scheme, Tx signals or Rx signals of the respective MSs are mixed in a plurality of channels. In this case, the BS and the plurality of MSs can distinguish the signals of the respective MSs by performing preceding on the Tx signals or by performing post-processing on the Rx signals. The preceding is an operation in which the Tx signal is multiplied by a Tx beamforming vector. The post-processing is an operation in which the Rx signal is multiplied by an Rx beamforming vector. For this, the BS determines the Tx beamforming vector and the Rx beamforming vector for the BS and each MS. The Tx beamforming vector and the Rx beamforming vector should satisfy a condition in which there is no interference between the MSs after Rx beamforming. Accordingly, there is a need for a method of determining an optimal Tx beamforming vector and an optimal Rx beamforming vector to perform effective spatial multiple access communication in the MIMO wireless communication system.